Electronic combine head float control system

ABSTRACT

An electronic control system for controlling the position of a combine harvesting head operable over a surface is disclosed herein. The position is controlled based upon the force or pressure at which the surface is supporting the implement. In particular, a hydraulic positioning assembly positions the head relative to the combine based upon control signals produced by a digital control circuit. The digital control circuit monitors digital signals representative of the force at which the surface is supporting the head, and compares these signals with digital setpoint data associated with a desired support force. Based upon the comparison, the control circuit produces control signals for causing the positioning assembly to raise or lower the harvesting head relative to the surface.

FIELD OF THE INVENTION

The present invention relates to controlling the position of aharvesting implement of an agricultural vehicle such as a combine. Inparticular, the present invention relates to an electronic controlsystem for controlling the position of a harvesting implement operatingover a surface. The position is controlled based upon the force orpressure at which the surface is supporting the implement.

BACKGROUND OF THE INVENTION

Systems for positioning harvesting heads relative to a combine aregenerally known. However, with the increasing need to improve harvestingefficiency while reducing harvesting time, it is important to increase acombine operator's control over the harvesting head. For example,automating the raising and lowering of a head increases the speed atwhich a combine can turn at the end of a cut. This type of automationmay also reduce waste by increasing the speed and accuracy at which thehead is lowered to resume cutting at the end of a turn. Automation alsoreduces operator fatigue by eliminating some of the control stepsrequired of an operator in conventional combines.

In addition to automation, it would be desirable to provide a combineoperator with the ability to effectively control the head position basedupon float control using digital electronic control system. Such acontrol system provides response speed sufficient to maintain the floatforce within a relatively narrow range of forces. This type of positioncontrol could be provided further utility with override modes to preventhead damage (e.g. when the force supporting the head goes too low,position or location control can be overridden).

Accordingly, the present invention provides an implement control systemwhich can provide a combine operator with one or more of the controlfeatures discussed above.

SUMMARY OF THE INVENTION

The present invention relates to an electronic implement float controlsystem useable in an agricultural vehicle such as a combine including amoveable implement for operation on a surface and a positioner formoving the implement in response to electric control signals. The systemincludes a force transducer for producing a force signal representativeof the support force at which the surface supports the implement, aconversion circuit coupled to the force transducer to produce digitalforce data representative of the force signal, and a digital processingcircuit coupled to the conversion circuit. The digital processingcircuit stores digital setpoint data representative of a selected,desired support force, compares the digital force data to the digitalsetpoint data, applies first electric control signals to the positionersuch that the implement is raised from the surface when the supportforce is greater than the desired support force, and applies secondelectric control signals to the positioner such that the implement islowered toward the surface when the support force is less than thedesired support force.

The present invention further relates to a combine including anelectronic implement float control system. The combine includes asupport structure for supporting the components of the combine, at leastfour wheels for movably supporting the combine on a surface andmechanically coupled to the support structure, an implement configuredto harvest plant related matter when the combine moves in a firstdirection, and an implement positioner coupled to the support structureto move the implement relative to the combine in response to electroniccontrol signals. The implement is supported by the support structure atthe front-most end of the combine relative to the first direction, andat least one of the wheels is powered to move the combine in the firstdirection. The combine further includes a force transducer coupled tothe implement to produce a force signal representative of the supportforce at which the surface supports the implement, a conversion circuitcoupled to the force transducer to produce digital force datarepresentative of the force signal, and a digital processing circuitcoupled to the conversion circuit. The digital processing circuit storesdigital setpoint data representative of a selected, desired supportforce, compares the digital force data to the digital setpoint data,applies first electric control signals to the positioner such that theimplement is raised from the surface when the support force is greaterthan the desired support force, and applies second electric controlsignals to the positioner such that the implement is lowered toward thesurface when the support force is less than the desired support force.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an agricultural vehicle including a moveableharvesting implement;

FIG. 2 is a schematic representation of the preferred embodiment of animplement position control system;

FIG. 3, including sheets 3A-3C, is a schematic diagram of the controlsystem circuitry; and

FIG. 4, including sheets 4A-4D, is a flow chart representative of theprogramming for the control system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an agricultural vehicle 10 includes a pair of drivewheels 12 located at the front end of vehicle 10, a pair of steerablewheels 14 located at the rear end of vehicle 10, a machinery and grainstorage compartment 16, a grain elevator and chute 18, an operator cab20, and a support frame (structure) for joining and supporting theabove-listed components. (By way of example only, vehicle 10 may be acombine of the type manufactured by Case Corporation having Model No.1660.) Attached to the front end of the frame of vehicle 10 (i.e. thefront-most end of vehicle 10 along its forward direction of travelduring harvesting) is an implement 22 such as a grain harvesting head.(By way of example, implement 22 could be a Combine Corn Head Series1000 sold by Case Corporation.) Implement 22 is positioned relative tovehicle 10 and/or the surface 23 upon which vehicle 10 is moving (i.e.the ground from which the respective plant related matter, grain orvegetation, is being harvested). To efficiently harvest the grain orvegetation, it is useful to provide control over the position orlocation of implement 22.

FIG. 2 is a schematic representation of the preferred embodiment of theimplement 22 position control system 24. Control system 24 includes amicroprocessor based control unit (circuit) 26, a man-controllerinterface 28, a vehicle direction and speed control lever 30, ahydraulic control valve 32, a position transducer 34, a locationtransducer 36, a pressure transducer 38, and an implement positioner(lift mechanism) 40 (e.g. hydraulic lift cylinders, cable liftarrangements, hydraulic motor and gear arrangements, or electric motorand gear arrangements). In the present embodiment, mechanism 40 includeshydraulic lift cylinders and transducers 34 and 36 are potentiometers.However, transducers 34 and 36 could be replaced with LVDTs, andtransducer 38 could be replaced by a current monitoring circuit if anelectric motor were used in mechanism 40.

Implement 22 is rotatably supported relative to vehicle 10 by a bearingassembly 42. Bearing assembly 42 includes a fixed bearing portion 44 anda movable bearing portion 46 fastened to implement 22. Fixed bearingportion 44 is fastened to vehicle 10 and to attachment member 45, andcontrol mechanism 40 is mounted between member 45 and a secondattachment member 47 fixed to implement 22. In this arrangement, system24 is operable to control mechanism 40 which moves (rotates) implement22 relative to vehicle 10. By way of modification, implement 22 can bemovably supported relative to vehicle 10 using other mechanicalarrangements such as, for example, a parallelogram linkage arrangementwhich supports implement 22 and, during raising and lowering, guidesimplement 22 along a path which is generally perpendicular to surface23.

Referring more specifically to system 24, interface 28 includes a modeswitch 48, a reference position (location) signal generator 50, areference pressure signal generator 52, a raise rate signal generator54, and a lowering rate signal generator 56. In the present embodiment,generators 50, 52, 54 and 56 are potentiometers. However, generators 50,52, 54 and 56 could be switches which are capable of producing digitalsignals representative of the associated positions, pressures and rates.

In addition to mode selector switch 48, system 24 also includes a raiseand lower switch 58 which is mounted in lever 30. By way of example,raise and lower switch 58 is a centrally biased momentary contactswitch. Switch 48 is coupled to unit 26 by a signal bus 60, generator 50is coupled to unit 26 by a signal bus 62, generator 52 is coupled tounit 26 by a signal bus 64, generator 54 is coupled to unit 26 by asignal bus 66, generator 56 is coupled to unit 26 by a signal bus 68,and switch 58 is coupled to unit 26 by a signal bus 70.

Control unit 26 is also coupled to transducer 34 by a signal bus 72,transducer 36 by a signal bus 74, and transducer 38 by a signal bus 76.Control unit 26 is coupled to hydraulic control valve 32 by a signal bus78. More specifically, control valve 32 includes a raise solenoid 80 anda lowering solenoid 82 to which signal bus 78 is connected. Control unit26 applies pulse width modulated signals to solenoids 80 and 82 whichallow valve 32 to control the flow of fluid between a pressurizedhydraulic fluid source 84 and lift cylinders 40. In the presentembodiment, source 84 is a hydraulic pump connected in series with ahydraulic fluid storage tank and appropriate filters.

Referring to FIG. 3 (3A, 3B, 3C) control unit 26 includes a digitalprocessor 86 (microcontroller, e.g. Motorola 80C198) having an internalanalog-to-digital converter 88, an analog-to-digital converter voltagereference source 90, a processor watchdog circuit 92, an analog signalfiltering and isolation circuit 94, an analog multiplexer 96, a switchinput control circuit 97, a serial communications interface 98, a memoryand a programmed logic control and memory circuit 100 (e.g. psd-312 soldby Wafer Scale Integration or Phillips/Sygnetics), a pulse width signalgeneration circuit 102, and a non-volatile memory 104.

Voltage reference source 90 (FIG. 3B) includes resistors 106 and 108,capacitors 110, 112 and 114, and operational amplifier 116 coupled tothe voltage reference and analog ground of processor 86 as shown. Source90 operates to provide a voltage range for analog-to-digital converter88 within which voltage signals are converted to digital values.

Processor watchdog circuit 92 (FIG. 3B) includes resistors 118, 120,122, 123 and 124, capacitors 126, 128 and 130, diode 132, low voltagedetector 134, inverter 136, and transistor 138 coupled to the reset ofprocessor 86 as shown. Circuit 92 resets processor 86 when the powersource 196 voltage falls below a predetermined level.

Analog multiplexer 96 (FIG. 3B) includes at least seven analog inputswhich are selectively coupled to an analog output 166, which is in turncoupled to the input of isolation circuit 94. Signal buses 62, 64, 66,68, 72, 74 and 76 are coupled to the analog inputs of multiplexer 96 byappropriate filtering circuits 152, 154, 156, 158, 160, 162 and 164,respectively. The analog inputs of multiplexer circuit 96 areselectively switched between the output 166 via a 4-bit data bus 168which is coupled to the output of control circuit 100. Accordingly,processor 86 selectively controls the application of the signals fromtransducers 34, 36 and 38 and signal generators 50, 52, 54 and 56 toanalog-to-digital converter 88 by applying the appropriate addresssignals to control circuit 100, which in turn applies the appropriate4-bit signal to data bus 168 for selectively applying the desired analogsignal to analog output 166.

Analog signal isolation circuit 94 (FIG. 3B) is coupled between output166 of multiplexer 96 and one analog input of analog-to-digitalconverter 88 to provide filtering and isolation there between. Circuit94 includes capacitors 140 and 142, operational amplifier 144, zenerdiode 146, diode 148 and resistor 150 coupled between output 166 and theanalog input channel of analog-to-digital converter 88 as shown.

As an alternate to the use of multiplexer 96, multiplexer 96 could beeliminated by using an analog-to-digital converter 88 with a sufficientnumber of analog input channels to handle the analog input signals fromtransducers 34, 36 and 38 and signal generators 50, 52, 54 and 56.However, such an arrangement increases the amount of circuitry requiredfor filtering and isolation since an isolation circuit 94 may berequired for all of the analog input channels to analog-to-digitalconverter 88. Thus, where sufficient sampling speed is obtained by usingmultiplexer 96 and a signal analog channel input to analog-to-digitalconverter 88, circuitry can be conserved since only one isolationcircuit 94 is necessary.

The statuses of switch 48 and switch 58 are monitored by processor 86via switch input control circuit 97, coupled between switch 48 andcircuit 97, and control circuit 100. More specifically, signal bus 60includes three conductors which are coupled to circuit 97 via anappropriate filtering circuit 170. Mode selector switch 48 includesthree contacts each connected to one of the three signal conductors ofbus 60, and selectively connected to a reference voltage (e.g. 12 volts)upon the status (position) of mode selector switch 48. When a signal isnot present on bus 60, switch 48 is assumed to be in the manualposition. Signal bus 70 includes two conductors connected to contacts inraise and lower switch 58 which are selectively connected to thereference voltage, depending upon the status of switch 58 (e.g., whenswitch 58 is in the uppermost position, one conductor is connected tothe reference voltage and when switch 58 is in the lowermost position,the other conductor is connected to the reference voltage). Signal bus70 is coupled to control circuit 97 by a filtering circuit 172. Inaddition to filtering circuit 172, further filtering is provided bycapacitors 174 and 176 coupled between the conductors of bus 70 andground.

Processor 86, circuit 97 and circuit 100 cooperate to sequentiallysample each of the conductors of signal buses 60 and 70. Morespecifically, circuit 97 operates as a storage and shift register tosample the statuses of the six signal conductors in signal buses 60 and70. Subsequently circuit 97 shifts through the memory locationassociated with each conductor, and sequentially applies a logic levelrepresentative of the status of each conductor to output data line 178in response to an input signal at input control line 180 and a clockingsignal at clock conductor 182. By way of example, when control line 180is HIGH, the register is cleared, and when control line 180 is LOW thestatuses of the six signal conductors are stored in the register and theregister is shifted left (or right depending upon the biasing of circuit97) in response to each clock pulse on line 182. Circuit 97 is coupledto processor 86 to sequentially apply the logic levels representative ofthe statuses of the signal conductors of signal buses 60 and 70 toprocessor 86 via data line 178.

Pulse-width generation circuit 102 (FIG. 3A) includes a solenoid coildriver circuit 184 (raising), a solenoid coil driver circuit 186(lowering), an AND gate 188, an AND gate 190, a flip flop 192, and apair of inverters 194 with hysteresis coupled together and to processor86 as shown in FIG. 3. Driver circuit 184 and 186 are conventionalcircuits for producing sufficient power to energize the coils of theraise solenoid 80 and the lowering solenoid 82 of control valve 32,respectively, based upon the output signals from AND gates 188 and 190,respectively.

The output of flip flop 192 is coupled to a first input of AND gates 188and 190. Flip flop 192 is connected to the PWM pin of processor 86 andapplies a logic HIGH signal to AND gates 188 and 190 at a frequencydetermined by the output of processor 86 applied to flip flop 192 (e.g.100 Hz) with a selectable pulse width. The second input to AND gate 188is coupled to one digital output of processor 86 and the second input ofAND gate 190 is coupled to another output of processor 86 to select oneof circuits 184 or 186. The width of the 100 Hz signal applied to coildriver circuits 184 and 186 from gates 188 and 189, respectively, isvaried to control the speed at which lift cylinders 40 are extended andcontracted (i.e., the rate of fluid flow from fluid source 84 to liftcylinders 40 depends upon the width of the pulse, where zero width meansno movement of cylinders 40 and maximum pulse width means movement ofcylinders 40 at their maximum speed), respectively. As a result, thespeed at which implement 22 can be raised and lowered can be varied byvarying the width of the pulse width modulated signal applied tosolenoids 80 and 82 by coil driver circuits 184 and 186, respectively.

Power for control unit 26 is provided from a conventional 5 V powersource 196. By way of example, power source 196 may include a 5 Vvoltage regulator and appropriate filtering coupled to the battery ofvehicle 10. Power from source 196 is provided to processor 86 viafiltering circuits 93 and 95. The clocking for processor 86 is providedby capacitors 87 and 89, and crystal 91 coupled together as shown inFIG. 3B.

Serial communications interface 98 (FIG. 3C) is provided to permitcommunication between control circuit 26 and other control systems ofvehicle 10. For example, interface 98 is configured to communicate witha display control circuit 220 configured to drive an alpha-numericdisplay 222 such as a LCD display. Interface 98 includes an inverterwith hysteresis 223, capacitors 224, 226 and 228, resistors 230, 232,234 and 236, and serial communication chip 238 (e.g. LT 1485N serialchip) coupled together between the transmit and receive pins ofprocessor 86 and display control circuit 220 as illustrated in FIG. 3.Display control circuit 220 is configured to format data transmittedfrom processor 86 by interface 98 to circuit 220 so that such data iscapable of producing the appropriate characters on display 222 located(e.g. within cab 20, see FIG. 1) for viewing by the combine operatorfrom within cab 20. By way of example, display 222 may have fourseven-segment characters and a decimal point between three of thecharacters and the fourth character. Alternatively, display 222 may alsoinclude icons and text segments in addition to the character segments.

In one embodiment of system 24, processor 86 is configured (programmed)to transmit data representative of the position of implement 22 asmonitored by potentiometer 34 to display control circuit 220 viainterface 98. In response to this data, circuit 220 controls display 222to produce a displayed value representative of the positionalrelationship between implement 22 and vehicle 10. Processor 86 isprogrammed to convert the position signal produced by potentiometer 34to data for controlling display 222 to display the height of implement22 in inches or centimeters.

Processor 86 can also be programmed to transmit data to display controlcircuit 220 which is representative of the signal produced bypotentiometer 36 which is in turn representative of the location ofimplement 22 relative to the ground surface 23. In response to thisdata, control circuit 220 controls display 222 to display a numericalvalue representative of the distance between bottom surface 206 ofimplement 22 and ground surface 23 (e.g. a distance having units ofinches or centimeters).

Additionally, processor 86 may also be programmed to transmit datarepresentative of the force (e.g. pounds or neutrons) being exerted bymechanism 40 on implement 22 to control circuit 220 via interface 98. Inparticular, processor 86 monitors transducer 38 and converts thehydraulic pressure into data representative of the float force requiredto maintain the position of implement 22 relative to vehicle 10 orground surface 23. This data is utilized by control circuit 220 toproduce a number representative of the force on display 222. By way ofexample, the force may be displayed as a percentage of the pressure whenimplement 22 is fully supported by surface 23 or mechanism 40.

Depending upon the application, processor 86 may be programmed toproduce display data representative of one or more of the locations ofimplement 22 relative to vehicle 10, the distance of implement 22relative to surface 23, or the force applied to implement 22. Where morethan one type of data is displayed, the icons and/or text segments canbe controlled to inform the operator of the type of data beingdisplayed. System 24 may be calibrated by setting high and low positionsof implement 22 relative to vehicle 10, high and low locations relativeto surface 23, and high and low forces applied by mechanism 40 by movingimplement 22 between the desired positions and locations, and byapplying a range of forces while in a calibration mode. Furthermore,processor 86 may be programmed to permit calibration of a range for thedisplay data.

The interaction of control circuit 26 with valve 32 for controlling theraising and lowering of implement 22 is described in detail below inreference to FIG. 4. The programming which configures (programs)processor 86 to provide appropriate control of the position of implement22, also described in reference to FIG. 4, is stored in memory circuit100. In general, control unit 26 controls the position of implement 22based upon the position (setting) of selector switch 48, the status ofswitch 58, the digital values produced by analog-to-digital converter 88representative of the settings of generators 50, 52, 54 and 56, and theanalog signals produced by transducers 34, 36 and 38.

As discussed above, transducers 34 and 36 are potentiometers in thepresent embodiment. Potentiometer 34 is mechanically coupled to alinkage arrangement 200 which rotates the wiper of potentiometer 34 toproduce a voltage representative of the positional relationship betweenimplement 22 and vehicle 10. Potentiometer 36 is mechanically coupled toa location sensor skid 202, located generally at the center of implement22, and to a cable arrangement 204 which move the wiper of potentiometer36 based upon the distance between the bottom 206 of implement 22 andthe surface 23 upon which skid 202 is resting. This arrangement ofpotentiometer 36, skid 202 and cable arrangement 204 produces a voltagerepresentative of the distance between bottom 206 and surface 23.Alternatively, depending upon the application, another type of proximitysensor such as an ultrasound sensor could be substituted forpotentiometer 36, skid 202 and cable assembly 204 to produce a signalrepresentative of the distance between bottom 206 and surface 23.

In the present embodiment, transducer 38 is a pressure transducer whichcommunicates with the fluid conduit which pressurizes lift cylinder 40to raise implement 22. This arrangement of pressure transducer 38produces a signal representative of the force being applied to implement22 for example, equal to some minimum value when the full weight ofimplement 22 is not being supported by surface 23.

System 24 can operate in a manual mode, return to cut (RTC) mode, afloat mode, and a height mode. In the manual mode, system 24 movesimplement 22 up and down in response to the operation of switch 58. Inthe height mode, system 24 maintains implement 22 at a selected locationrelative to surface 23. In the float mode, system 24 maintains implement22 at a selected contact pressure with surface 23. In the RTC mode,system 24 allows the user to raise implement 22 from a predeterminedposition by toggling switch 58 upward (typically at the end of a row ina field) and then automatically return to the position by togglingswitch 58 downward (typically at the beginning of a row in the field).

FIG. 4 (4A, 4B, 4C, 4D) illustrates the sequence of steps whichprocessor 86 is programmed (configured) to carry out while operating inone of the manual, RTC, float or height modes. Each time processor 86completes the sequence of steps specified by FIG. 4, processor 86 clocksthe first inputs of AND gates 188 and 190 (FIG. 3), and applies theappropriate pulse-width signal to the other inputs of AND gates 188 and190. For example, if upon executing all of the instructions associatedwith the flow chart of FIG. 4, a decision is made to raise implement 22,0 width pulses would be applied to AND gate 190 so that coil drivercircuit 186 is inoperative, and pulses of appropriate widths would beapplied to AND gate 188 to cause coil driver circuit 184 to open valve32. In response, valve 32 applies pressurized fluid to lift cylinders 40to raise implement 22.

As discussed in detail below, when implement 22 is moved by system 24,the speed of movement is based upon the difference between the selectedposition and the desired position, the selected height and the actualheight, or the selected float pressure and the actual float pressure(e.g., proportional control). Thus, when the difference is large, theerror is large, and the width of the pulses applied to the appropriateAND gate 188 or 190 is correspondingly large. As the implement is movedtoward the desired position, height location or float position, theerror is reduced, the width of the pulses applied to the appropriate ANDgate 188 or 190 is reduced to slow the speed at which implement 22 ismoved, and the speed of implement 22 goes to zero when the desiredsetpoint is reached.

In operation, processor 86 samples the status of selector switch 48 viashift register 97 and circuit 100 to determine the mode of operation forsystem 24 (step 250, startup). Next, processor 86 determines the digitalvalue associated with signal generators 50 and 52 (step 252). The analogvalues produced by generators 50 and 52 are applied to analog-to-digitalconverter 88 via multiplexer 96 and filtering circuit 94. Depending uponthe mode selected at switch 48, processor 86 stores the digital valueproduced by analog-to-digital converter 88 representative of theposition of generator 50 as the desired height or position value, andthe digital value produced by converter 88 representative of theposition of generator 52 as the desired float value.

In step 254, processor 86 controls multiplexer 96 via databus 168 toapply the signals produced by potentiometers 34 and 36, and transducer38, to converter 88 via multiplexer 96 and isolation circuit 94. Uponapplying the respective signals produced by transducers 34, 36 and 38 toconverter 88, the digital values produced by converter 88 are stored byprocessor 86 in the memory of circuit 100.

In step 256, processor 86 determines if momentary switch 58 has beenmomentarily actuated to the lower most position (e.g. 0.1-0.6 seconds).If such a condition has occurred, soft-lower flag is set. In step 258,processor 86 controls multiplexer 96 via bus 168 to apply the analogsignals produced by generators 54 (maximum raise rate signal, e.g. 2-10seconds for implement 22 raising) and generator 56 (maximum lower ratesignal, e.g. 2-10 seconds for implement 22 lowering) toanalog-to-digital converter 88 via filtering circuit 94. Processor 86stores the digital values produced by converter 88 representative of themaximum raise and lower rates in circuit 100. Based upon the maximumraise and lower rate signals, processor 86 calculates and storesacceleration and deceleration values representative of the accelerationsbetween zero speed of implement 22 and the selected raise and lowerrates. By appropriately accelerating and decelerating implement 22 viacontrol unit 26, relatively smooth motion of implement 22 is achievedeven though hydraulic accumulators are either eliminated from system 24or reduced in size.

The raise and lower rate acceleration values are stored as values whichprogressively increase to the maximum raise/lower rate values, and theraise and lower rate deceleration values are stored as values whichprogressively decrease from the maximum raise/lower rate values to zero.The acceleration values are used by processor 86 to increase (ramp up)the pulse widths from zero to the maximum associated with the maximumrate during the acceleration period for implement 22 (e.g. 0.1-0.5seconds), and the deceleration values are used by processor 86 todecrease (ramp down) the pulse widths from the maximum to zero duringthe period of deceleration of implement 22 (e.g. 0.1-0.5 seconds).

In step 260, processor 86 reads data stored in memory 100 representativeof the state (selected mode) of switch 48 and executes the subroutineassociated with the selected mode. In step 262, processor 86 defaults tothe manual mode. In step 264, if switch 48 is set to the height mode, ifthe soft lower flag is set, and if the desired height value as generatedby generator 50 is less than the height value sensed at potentiometer36, processor 86 sets a flag for the "to height mode" subroutine (step266) and the lower feeder subroutine is called (step 268). The lowerfeeder subroutine sets the width of the pulses applied to valve 32 forlowering implement 22 based upon pressure or position error or a fixedwidth based upon the setting of generator 56 when in the manual mode.

If switch 48 is not set to the height mode or the desired height valueis greater than the height value representative of the signal frompotentiometer 36, processor 86 executes step 270. In step 270, if switch48 is set to the float mode, if the soft lower flag is set, and if thedesired float value produced by generator 52 is less than the sensedfloat value produced by transducer 38, processor 86 sets a flag for the"to float mode" subroutine (step 272) and the lower feeder subroutine iscalled (step 268). It should be noted that the sensed float valuereferred to here corresponds to the pressure in cylinders 40 required tosupport implement 22. Thus, lowering implement 22 has the effect oflowering the sensed float value by allowing implement 22 to be supportedto a greater degree by surface 23. If switch 48 is not set to the floatmode, or the desired float value is greater than the valuerepresentative of the signal produced by transducer 38, processor 86executes step 274.

In step 274, processor 86 determines if switch 48 is set to the RTCmode, if the soft lower flag is set, and if the desired position valuerepresentative of the signal produced by generator 50 is less than thefeeder position value representative of the signal produced bypotentiometer 34, processor 86 sets the control position subroutine flag(step 276) and the lower feeder subroutine is called (step 268). If anyof the conditions in step 274 are not true, processor 86 defaults to themanual mode and samples the status of switch 58 to determine if switch58 has been toggled to the raise or lower position (steps 278 and 280).If switch 58 is in the raise position, the raise feeder subroutine iscalled (step 282), and if switch 58 is in the lower position, the lowerfeeder subroutine is called (step 284). The raise feeder subroutine setsthe width of the pulses applied to valve 32 for raising implement 22based upon position error, or a fixed width when in the manual mode.

While system 24 is operating in the return to cut mode, and implement 22is operating in the position selected for cutting, as represented by thesignal produced by generator 50, the "control position" subroutine isexecuted by processor 86. In step 286, processor 86 begins executing the"control position" subroutine. In step 288, switch 58 is sampled todetermine whether or not the operator is attempting to manually controlthe location of implement 22. If switch 58 has been operated, processor86 goes into the manual mode and executes a combination of steps 278,280, 282 and 284 (step 290). If switch 58 was not operated, processor 86calculates the difference between the desired position value and theposition value representative of the signal generated by potentiometer34 to produce a position error value (step 292). If the position errorindicates that implement 22 is too low (step 294), the raise feedersubroutine is called (step 296). If processor 86 determines thatimplement 22 is not too low (error high), processor 86 compares thedesired float sensor value to the float sensor value representative ofthe signal produced by pressure transducer 38 (step 298). If processor86 determines that the float error represents a float pressure lowerthan the desired pressure (steps 300 and 302, again referring to thepressure or force by surface 23 tending to raise implement 22, i.e. asurface 23 support force greater than the desired support force), theraise feeder subroutine is called (step 296). If processor 86 calculatesa float error which represents that the float pressure is higher thanthe desired float pressure (step 304), the lower feeder subroutine iscalled (step 306). Upon completion of the control position routine,switch 58 is again sampled by processor 86 (steps 278 and 280) and theraise and lower feeders subroutines are appropriately called (steps 282and 284). (Steps 298, 300, 302, 304 and 306 provide float controloverride of position control.)

The "to height mode" subroutine (step 308) is entered when the heightmode has been set in step 266 as discussed above. In the "to heightmode" subroutine, switch 58 is sampled (step 310) and if the raisedposition of switch 58 has been toggled, processor 86 goes into themanual mode and executes a combination of steps 278-284 (step 312). Instep 314, processor 86 determines whether or not a setting is present inmemory 100 representative of the position of implement 22 associatedwith a particular height setpoint value (i.e. feeder found flag is set)as determined in step 252. Upon startup of vehicle 10, a position valueassociated with the desired height value will not be present in memory100. When a position value is not available (i.e. the feeder found flagis not set), processor 86 determines the difference between the desiredheight value representative of the position of generator 50 and theactual height value representative of the value produced bypotentiometer 36 (step 316).

In step 314, when a position value associated with the height value isnot available, a flag is set by processor 86 to reduce the size of thepulse widths applied to AND gates 188 or 190. This is done so thatimplement 22 is moved relatively slowly while being moved toward thedesired height. This prevents jerking of implement 22 since skid 202,linkage 204 and potentiometer 36 do not begin producing a meaningfulsignal until skid 202 comes in contact with the ground. In step 316, ifthe height value representative of the signal at potentiometer 36 isgreater than the desired height value representative of the signalproduced by generator 50, the lower feeder subroutine is called (step322). When the sensed height value is less than the desired heightvalue, the height mode flag is set (step 318).

If processor 86 determines that a position value associated with thedesired height value is stored in memory 100, processor 86 calculatesthe error between the position value representative of the signalproduced by potentiometer 34 and the position value associated with thedesired height (step 324). In step 326, the processor calls the raisefeeder subroutine (step 320) if the error represents the location ofimplement 22 which is too low for the associated height, and in step328, if the error is high, calls the lower feeder subroutine (step 322).If the error is neither high nor low, processor 86 sets the height modeflag (step 330). In general, while running the "to height subroutine,"processor 86 controls the operation of lift cylinders 40 usingpotentiometer 34 (i.e. position control) until implement 22 is at aposition within a range defined by high and low error bands (e.g. within±1.5% to 2% of the desired position) at which time processor 86 entersthe height mode subroutine (step 332) to begin controlling the locationof implement 22 relative to surface 23 based upon the signal generatedby potentiometer 36 (i.e. height or location control).

The "height mode" (step 332) subroutine is entered in response toprocessor 86 setting a height mode flag in steps 318 or 330. In step 333the feeder found flag is cleared. In step 334, processor 86 determineswhether or not switch 58 has been toggled to the raise position. Ifswitch 58 has been toggled to the raise position, then processor 86 goesinto the manual mode (step 336) and sets the feeder position valueassociated with the desired height stored in memory 100 to the positionvalue representative of the signal produced by potentiometer 34 (step338). In step 340, processor 86 sets a feeder found flag which is testedby processor 86 in step 314 to determine whether or not a position valuerepresentative of the desired height is stored in memory 100. In step334 if switch 58 has not been toggled to the raise position, processor86 determines if switch 58 has been toggled to the lower position (step342). If switch 58 has been toggled to the lower position, the lowerfeeder subroutine is called in step 284. If switch 58 has not beentoggled to the lower position, processor 86 samples the height valuerepresentative of the signal produced by potentiometer 36, compares thisactual height value to the desired height value representative of thesignal produced by generator 50, and calculates a height error value(step 344). If the error value indicates that implement 22 is too low,the raise feeder subroutine is called (step 346 and 348), if the errorsignal indicates that implement 22 is too high, the lower feedersubroutine is called (steps 350 and 352). If the error calculated isbetween the low error value (step 346) and the high error value (step350), processor 86 does not call either the raise or lower feedersubroutines. After steps 340, 342, 348 or 352 have been executed,processor 86 samples the status of switch 58 at steps 278 and 280, andreturns to the start of the program (step 254).

The "to float mode" subroutine (step 356) is entered in response to thesetting of the "to float mode" flag at step 272 discussed above. In the"to float mode," switch 58 is sampled (step 358) and if the raisedposition of switch 58 has been toggled, processor 86 goes into themanual mode and executes a combination of steps 278-284 (step 360). Instep 362, processor 86 determines whether or not a setting is present inmemory 100 representative of the position of implement 22 associatedwith a particular float setpoint value (i.e. checks the float feederfound flag). (Upon startup of vehicle 10, a position value associatedwith the desired float value will not be present in memory 100.) Where aposition value is not available, processor 86 determines the differencebetween the desired float value representative of the position ofgenerator 52 and the actual float value representative of the signalproduced by pressure transducer 38 (step 364).

In step 362, when a position value associated with the float value isnot found (i.e. float feeder found flag set), a flag is set by processor86 to reduce the size of the pulse widths applied to AND gates 188 or190 during the execution of the lower feeder flag subroutine. This isdone so that implement 22 is moved relatively slowly while being movedtoward the desired float pressure. This reduces jerking of implement 22since the float value representative of the signal produced bytransducer 38 changes abruptly when bottom 206 of implement 22 comes incontact with the ground. If the sensed float value is greater than thedesired float value, the lower feeder subroutine is called (step 368).In step 364, if the float value representative of the signal attransducer 38 ("sensed float value") is less than the desired floatvalue representative of the signal produced by generator 52, the floatmode flag is set (step 366).

If processor 86 determines that a position value associated with thedesired float value is stored in memory 100 (i.e. float feeder foundflag set), processor 86 calculates the error between the position valuerepresentative of the signal produced by potentiometer 34 and theposition value associated with the desired float value (step 370). Instep 372, processor 86 calls the raise feeder subroutine (step 374) ifthe error represents the location of implement 22 which is too low forthe associated float value. In step 376, if the error is high, theprocessor 86 goes to step 368 to call the lower feeder subroutine. Ifthe error is between the high and low limit values, processor 86 setsthe float mode flag (step 378).

In general, while running the "to float mode" subroutine, processor 86controls the operation of lift cylinders 40 using potentiometer 34 untilimplement 22 is at a position within a range defined by the high and lowerror values associated with the selected float pressure. Subsequently,processor 86 can enter the "float mode" subroutine to begin controllingthe location of implement 22 relative to surface 23 based upon thesignal generated by transducer 38 (float control).

The "float mode" (step 380) subroutine is entered in response toprocessor 86 setting a float mode flag in steps 366 or 378. In step 381the float feeder found flag is cleared. In step 382, processor 86determines whether or not switch 58 has been toggled to the raise orlower position. If switch 58 has been toggled to the raise or lowerposition, then processor 86 goes into the manual mode (step 384) andsets the feeder position value associated with the desired float to theposition value representative of the signal produced by transducer 34(step 386). Processor 86 then sets a float feeder found flag (step 388)which is tested by processor 86 in subsequent loops through the programat step 362 to determine whether or not a position value associated withthe desired float value is stored in memory 100.

If switch 58 has not been toggled, processor 86 samples the float valuerepresentative of the signal produced by transducer 38, compares thefloat value to the desired float value representative of the signalproduced by generator 52, and calculates a float error value (step 390).If the error value indicates that implement 22 is too low (i.e. that thepressure currently exerted to support implement 22 is too low), theraise feeder subroutine is called (steps 392 and 394), if the errorsignal indicates that implement 22 is too high (i.e. that cylinders 40are currently supporting implement 22 to an extent greater thandesired), the lower feeder subroutine is called (steps 396 and 398). Ifthe error calculated is between a low error value (step 392) and a higherror value (step 396), processor 86 does not call either the raise orlower feeder subroutine. After processor 86 samples the status of switch58 at steps 278 and 280, processor 86 returns to the start of theprogram (step 254).

Upon reaching step 354 (FIG. 4D), processor 86 will have calculated apulse width, and stored the values of the pulse width in memory 100. Themaximum width of the pulse width value for raising and loweringimplement 22 via the control of lifting cylinders 40 by control valve 32is determined by processor 86 from the digital values representative ofthe settings of generators 54 and 56, respectively. Based upon the rangeof pulse width values available for controlling the speed of raising andlowering and the error signal, processor 86 calculates the raise orlower pulse width values when the raise and lower feeder subroutines(steps 282 and 284) are called. Thus, for a very high error signalvalues, processor 86 will use the maximum pulse width values, and for anerror signal value approaching zero, processor 86 will use a relativelyshort duration pulse width values.

Each time processor 86 goes through the control sequence represented inFIG. 4 and reaches step 354, the pulse width modulated signal having awidth calculated when the raise or lower subroutine is called, isapplied to the appropriate AND gate 188 or 190 depending upon whether ornot implement 22 is to be raised or lowered. If implement 22 is to beraised, AND gate 188 is pulsed by processor 86 to drive coil driver 184which pulses valve solenoid 80 of valve assembly 32 to pressure liftcylinders 40 and thereby raise implement 22. If implement 22 is to belowered, processor 86 applies a pulse width modulated signal to AND gate190 which applies the pulse width signal to coil driver circuit 186which pulses valve solenoid 82 of valve assembly 32 to allow hydraulicfluid to flow from lift cylinders 40 and thereby lower implement 22.Subsequent to pulsing the appropriate gate 188 or 190, processor 86 goesback to step 250 and executes the control sequence represented in FIG.4.

It will be understood that the description above is of the preferredexemplary embodiment of the invention and that the invention is notlimited to the specific forms shown and described. For example, thecontrol system is disclosed in reference to a grain harvesting device;however, the system may also be utilized with other harvesting devicessuch as cotton pickers. Furthermore, depending upon the application, thevarious communication links which are hardwired for data and signalcommunication could be replaced with appropriate wireless communicationhardware. Another modification to the system includes providing apotentiometer 36 and skid arrangement 202 at both ends of implement 22and coupling the second potentiometer to an eight input multiplexer 96.Using this arrangement, processor 86 can be programmed to monitor bothpotentiometers 36 and use the signals from both potentiometers 36 tocontrol the location of implement 22. For example, processor 86 may beprogrammed to generate a height value for implement 22 relative tosurface 23 by (1) averaging the signals from potentiometers 36, (2)using the greatest value from potentiometers 36, or (3) using the lowestvalue from potentiometers 36. Since implement 22 can typically be over30 feet long, and surfaces 26 can be relatively uneven over such awidth, implement 22 location control can be improved by using more thanone location sensor such as discussed above. As a further modification,a plurality of potentiometers (e.g. four) and skid arrangements 202could be spaced along implement 22, where a logic circuit is coupled tothe potentiometers and only outputs the value from the potentiometerassociated with the lowest portion of implement 22 to circuit 96.

Other substitutions, modifications, changes and omissions may be made inthe design and arrangement of the preferred embodiment without departingfrom the spirit of the invention as expressed in the appended claims.

What is claimed is:
 1. In an agricultural vehicle including a moveableimplement for operation on a surface and including a positioner formoving the implement in response to pulse-width modulated controlsignals at velocities dependent upon the duration of the pulses of thecontrol signals, an electronic implement float control systemcomprising:a force transducer coupled to the implement to produce aforce signal representative of the support force at which the surfacesupports the implement; a conversion circuit coupled to the forcetransducer to produce digital force data representative of the forcesignal; and a digital processing circuit coupled to the conversioncircuit to store digital setpoint data representative of a desiredsupport force, compare the digital force data to the digital setpointdata, apply first pulse-width modulated control signals to thepositioner, the control signals having pulse durations dependent on thecomparison, such that the implement is raised from the surface at avelocity dependent on the comparison when the support force is greaterthan the desired support force, and apply second pulse-width modulatedcontrol signals to the positioner, the control signals having pulsedurations dependent on the comparison, such that the implement islowered toward the surface at velocities dependent on the comparisonwhen the support force is less than the desired support force.
 2. Thesystem of claim 1, wherein the force transducer is a pressuretransducer.
 3. The system of claim 2, further comprising a humaninterface configured to selectively produce desired force signalsrepresentative of desired support forces, the conversion circuit beingan analog-to-digital converter coupled to the pressure transducer andthe human interface, wherein the analog-to-digital converter convertsthe desired force signals to the digital setpoint data.
 4. The system ofclaim 3, wherein the digital processing circuit comprises:amicroprocessor coupled to the analog-to-digital converter; a memorycoupled to the microprocessor for storing the digital setpoint data; anda pulse-width modulation circuit coupled to the microprocessor, thepulse-width modulation circuit producing the first and secondpulse-width modulated control signals.
 5. The system of claim 4, whereinthe microprocessor is configured to control the pulse-width inproportion to the difference between the support force and the desiredsupport force.
 6. In an agricultural vehicle including a moveableimplement for operation on a surface and including a positioner formoving the implement in response to pulse-width modulated signals atvelocities dependent on the duration of pulses of the signals, anelectronic implement float control system comprising:transducer meansfor producing a force signal representative of the support force atwhich the surface supports the implement; conversion means for producingdigital force data representative of the force signal; and digitalprocessing means for storing digital setpoint data representative of adesired support force, comparing the digital force data to the digitalsetpoint data, applying first pulse-width modulated signals having pulsedurations dependent on the comparison to the positioner such that theimplement is raised from the surface at velocities dependent on thecomparison when the support force is greater than the desired supportforce, and applying second pulse-width modulated signals having pulsedurations dependent on the comparison to the positioner such that theimplement is lowered toward the surface at velocities dependent on thecomparison when the support force is less than the desired supportforce.
 7. The system of claim 6, wherein the transducer means is apressure transducer.
 8. The system of claim 7, further comprising ahuman interface configured to selectively produce desired force signalsrepresentative of desired support forces, the conversion means being ananalog-to-digital converter coupled to the pressure transducer and thehuman interface, wherein the analog-to-digital converter converts thedesired force signals to the digital setpoint data.
 9. The system ofclaim 8, wherein the digital processing means comprises:a microprocessorcoupled to the analog-to-digital converter; a memory coupled to themicroprocessor for storing the digital setpoint data; and a pulse-widthmodulation circuit coupled to the microprocessor, the pulse-widthmodulation circuit producing the first and second pulse-width modulatedcontrol signals.
 10. The system of claim 9, wherein the microprocessoris configured to control the pulse-width in proportion to the differencebetween the support force and the desired support force.
 11. A combinecomprising:a support structure for supporting the components of thecombine; at least four wheels for movably supporting the combine on asurface and mechanically coupled to the support structure, at least oneof the wheels being powered to move the combine in a first direction; animplement configured to harvest plant related matter when the combinemoves in the first direction, the implement being movably supported bythe support structure at the front-most end of the combine relative tothe first direction; an implement positioner coupled to the supportstructure to move the implement relative to the combine in response toelectronic control signals; a force transducer coupled to the implementto produce a force signal representative of the support force at whichthe surface supports the implement; a conversion circuit coupled to theforce transducer to produce digital force data representative of theforce signal; and a digital processing circuit coupled to the conversioncircuit to store digital setpoint data representative of a desiredsupport force, compare the digital force data to the digital setpointdata, apply first pulse-width modulated control signals to thepositioner, the control signals having pulse durations dependent on thecomparison, such that the implement is raised from the surface at avelocity dependent on the comparison when the support force is greaterthan the desired support force, and apply second pulse-width modulatedcontrol signals to the positioner, the control signals having pulsedurations dependent on the comparison, such that the implement islowered toward the surface at velocities dependent on the comparisonwhen the support force is less than the desired support force.
 12. Thecombine of claim 11, wherein the implement positioner comprises:apressurized hydraulic fluid source; at least one hydraulic lift cylinderin fluid communication with the fluid source and coupled between thecombine and implement; and a control valve disposed to couple thecylinder to the fluid source, the valve including control solenoids. 13.The combine of claim 12, wherein the force transducer is a pressuretransducer in fluid communication with the hydraulic lift cylinder. 14.The combine of claim 13, further comprising a force setpoint signalgenerator configured to produce force setpoint signals.
 15. The combineof claim 14, further comprising a solenoid driver circuit coupled to thecontrol solenoids, wherein the conversion circuit is ananalog-to-digital converter coupled between the transducer and thedigital processor to convert the force signals to digital force data andconvert the setpoint signals to digital setpoint data.
 16. The combineof claim 15, wherein the digital processing circuit comprises:amicroprocessor coupled to the analog-to-digital converter; a memorycoupled to the microprocessor for storing the digital setpoint data; anda pulse-width modulation circuit coupled to the microprocessor and thesolenoid driver, the pulse-width modulation circuit applying the firstand second pulse-width modulated control signals having a selectablepulse-width and a predetermined frequency to the solenoid driver. 17.The system of claim 16, wherein the microprocessor is configured tocontrol the pulse-width in relation to the difference between thesupport force and the desired support force.
 18. The system of claim 16,wherein the microprocessor is configured to control the pulse-width inproportion to the difference between the support force and the desiredsupport force.
 19. The combine of claim 11, wherein the implementpositioner comprises:a pressurized hydraulic fluid source; a pluralityof hydraulic lift cylinders in fluid communication with the fluid sourceand coupled between the combine and implement; and a control valvedisposed to couple the cylinders to the fluid source, the valveincluding control solenoids coupled to the digital processing circuit.20. The combine of claim 19, wherein the force transducer is a pressuretransducer in fluid communication with the hydraulic lift cylinders.